1. Field of the Invention
The invention relates generally to vertical impact crushers for crushing brittle and typically abrasive materials such as rocks and the like, and more particularly to vertical shaft impact crushers which include vertically adjustable feed tubes.
2. Discussion of the Prior Art
A typical vertical shaft impact crusher employs an impeller rotor or table at the upper end of a vertical, driven shaft. The rotor revolves in a housing into which material to be crushed is supplied from a feed hopper through a generally vertical "feed tube". The feed tube extends from the feed hopper downward through a lid of the crusher and has an opening at its lower end adjacent the table of the crusher. The lower end of the feed tube is subject to relatively rapid wear from the swirling material as it strikes the feed cone or the like about the center of the table. Consequently, the feed tube must be periodically lowered in order to maintain a proper relationship to the crusher's table. Traditionally that adjustment has been effected by spacer blocks between a flange at the upper end of the feed tube and a flange in the feed hopper. After the feed tube is worn beyond an acceptable limit, the tube is pulled up out of the hopper, the built-up material between the tube, spacers and hopper is cleaned out, one or more of the spacer blocks is removed, and the feed tube reinstalled, all steps constituting a laborious and time-consuming job.
Without the feed tube or with improper vertical adjustment of the feed tube to an optimum spacing between a top table surface of the impeller rotor and the lowermost end of the feed tube, the crusher fails to operate properly. In accordance with the prior art practices a spare feed tube may be mounted back to back to an operationally adjusted feed tube extending to just above the rotor or impeller table. The spare feed tube typically extends into the crusher feed hopper to support a peripheral thickness of rock materials and reduce wear of hopper walls. When the active feed tube is worn beyond acceptable limits, the spare feed tube may be substituted for the active feed tube to restart the adjustment process described above.
Another approach is shown in U.S. Pat. No. 4,513,919 to Terrenzio in which a rather elongated feed tube is slidably disposed within the feed hopper which is mounted on brackets attached to the crusher lid. The tube is encircled below the hopper by a releasable clamp, the clamp in turn being separately supported from the crusher lid on upright threaded studs having pairs of nuts between which the clamp is captured. The clamping hold on the feed tube may be released for an up and down adjustment of the feed tube. It is understood that in typical impact crushers, a feed tube is of a substantial weight, the weight making the vertical adjustment of the feed tube a rather complex procedure. When the feed tube is worn beyond acceptable limits, the entire tube, since it is one piece, needs to be replaced by releasing the clamp and lifting the tube out through the hopper. As with other known adjustable feed tubes, the last described adjustment provision does not address a problem of the remaining upper half of the feed tube when the lower portion has worn and feed tube has been adjusted to its lowermost position. Thus the upper portion of the feed tube is typically considered a wasted remainder. Also, because of dust and fines which are present during the crushing operation, bolt threads are likely to become damaged or begrimed making the threaded fasteners, such as for clamping the feed tube, difficult to turn. In view of the above described continuing difficulties in making adjustments to feed tubes of the described crushers, it is an object of the present invention to provide an adjustable feed tube for a vertical shaft impact crusher which alleviates above referred to disadvantages and which further improves the state of the art by facilitating the adjustment of the feed tubes of vertical shaft impact crushers and by allowing the feed tubes to be adjusted in a predictable manner from the outside of the crushers. Another object of the invention is to provide a feed tube of which an unused remainder of the feed tube after final adjustment of the feed tube is minimized.